1. Field of the Invention
The present invention relates to a fuel injection device.
2. Description of Related Art
For example, Japanese Unexamined Patent Publication Number 2000-73918 discloses one type of fuel injection device (also referred to as an injector). With reference to FIG. 13, in this fuel injection device, fuel is injected through injection holes 156 formed through a planar injection hole plate 152. In general, in such a fuel injection device, it is possible to increase a level of atomization by enhancing agitation of fuel flow through the injection holes. When fuel flows through each injection hole, which extends in a fuel injection direction, the injection hole tends to stratify the fuel flow. Thus, when the length of the injection hole in its passage direction is reduced, atomization of fuel mist can be further promoted. Because of this, when the planar injection hole plate 152 is thinned to reduce the length of the injection hole 156 in its passage direction, the atomization of fuel mist can be further promoted.
However, when the injection hole plate is thinned, there is an increased possibility of fatigue destruction of the injection hole plate caused by the fuel pressure. Thus, when the injection hole plate is thinned, the injection hole plate should be reinforced by another member. Particularly, in a case of a fuel injection device, which directly injects fuel into a corresponding combustion chamber of a gasoline engine, fuel pressure reaches 5–12 MPa, which is 16 to 40 times greater than that of a fuel injection device, which injects fuel into an intake pipe, so that it is required to provide a sufficient strength in the injection hole plate.
For example, in the fuel injection device shown in FIG. 13, a retainer plate 154 is provided adjacent to a downstream end surface of the injection hole plate 152, which is located on a side opposite from a valve body 150. The retainer plate 154 is welded to a cylindrical sleeve 158, which is, in turn, welded to the valve body 150. In this way, the injection hole plate 152 is secured relative to the valve body 150. Through reinforcement of the injection hole plate 152 by the retainer plate 154, even when the injection hole plate 152 is thinned to some degree, sufficient safety of the injection hole plate 152 against fatigue destruction can be achieved by the retainer plate 154.
However, for example, in the case of the retainer plate 154 and the sleeve 158 shown in FIG. 13, the number of components is increased, disadvantageously resulting in an increased structural complexity and an increased manufacturing costs. Furthermore, the assembly operation of the plates are tedious, and thus industrial productivity of the fuel injection device is reduced.
Also, in the Japanese Unexamined Patent Publication Number 2000-73918, there is also disclosed another type of fuel injection device, in which the injection hole plate and the retainer plate are both welded to the valve body. In this fuel injection device, the plates are welded to the valve body at once while the plates are partially overlapped with each other. Thus, energy consumption at the time of welding is disadvantageously increased to increase the manufacturing costs, and the time required for welding is also disadvantageously lengthened, resulting in the reduced industrial productivity of the fuel injection device.